Yes I totally agree with this request. Although in previous versions of Evernote (on a MAC at least) this was available from a menu point, it seems to have disappeared as of a couple of months ago (currently on 10.5.7). This is a show stopper for me and I presume many others who work in more than one language and need to constantly change from one to the other.
On many MAC apps, this language switcher is accessed by the handy Command-Shift-: . It would be very nice if Evernote did the same, but I'd settle for the old menu point to bring up the language switcher to save the day.